I don't think it is possible but...

[Hafenguy]

Is there a way to convert the civ 5 units in civ 4?
I mean that there are not only 3 (or1) Fighters who represent a unit. I would like to have as much Fighters as in civ 5 which really looks more like an army than just 3 Fighters.

 

[ramzay1945]

If I understood correctly what exactly you want, then look at this
https://forums.civfanatics.com/resources/zlatko-mini-formation-mod.20141/

 

[PPQ_Purple]

Changing how many models are shown in a unit is actually a fairly easy XML job. All you have to do is find this bit of the XML in the units unit_art_define and change this bit:

            <UnitMeshGroups>
                <iGroupSize>3</iGroupSize>
                <fMaxSpeed>1.75</fMaxSpeed>
                <fPadTime>1</fPadTime>
               <iMeleeWaveSize>3</iMeleeWaveSize>
                <iRangedWaveSize>0</iRangedWaveSize>
                <UnitMeshGroup>
                    <iRequired>3</iRequired>
                    <EarlyArtDefineTag>ART_DEF_UNIT_INFANTRY</EarlyArtDefineTag>
                </UnitMeshGroup>
            </UnitMeshGroups>

You can even create combination units like 2 infantry and 1 tank and stuff by editing this.